Various systems and arrangements to determine knocking or pinging of an IC engine are known; one such system is described in U.S. Pat. No. 4,106,447. As described, a knocking sensor generates a signal which includes signal components representative of knocking oscillations and background and noise signals. The composite signal is applied to a demodulator which has a background signal branch and a knocking signal branch. The demodulator circuit is connected to a comparator. The background noise signal is separated by a low-pass filter. Comparison of the background noise signal with the knocking signal in the comparator results in a digital output signal representative of "yes"/"no" regarding knocking conditions. Disturbance or noise signals which occur during the time of knocking, and within a measuring window range, cannot be eliminated, however, and may be recognized as knocking signals, although knocking, itself, did not occur. Such background or noise signals which may, erroneously, be considered as knocking signal, could be generated by mechanical impacts to which the knock sensor is subjected, for example by impacts having steep flanks, and caused, for example, by noise signals due to piston operation of the IC engine.